1. Field of the Invention
This invention relates to Si.sub.3 N.sub.4 -Al.sub.2 O.sub.3 composite sintered bodies and a method of producing the same. More particularly the invention relates to Si.sub.3 N.sub.4 -Al.sub.2 O.sub.3 composite sintered bodies suitable for use in structural materials having high strength at high temperature and a method of producing the same.
2. Related Art Statement
Al.sub.2 O.sub.3 is widely used as a substrate or a package for integrated circuits, a chip for cutting tools or a refractory material. However, the strength of Al.sub.2 O.sub.3 at a temperature of not lower than 1,000.degree. C. is low compared to a silicon nitride sintered body and silicon carbide sintered body, so that there is a restriction in the use of Al.sub.2 O.sub.3 as a structural material for engine parts and the like.
In order to increase the strength and toughness of Al.sub.2 O.sub.3, it has been proposed to disperse SiC whiskers into the Al.sub.2 O.sub.3. For example, increasing the toughness of the Al.sub.2 O.sub.3 sintered body through dispersion of SiC whiskers is disclosed in American Ceramics Society Bulletin, 64[2], 298-304 (1985). However, when this sintered body is heated in air, the oxidation of SiC violently occurs to lower the strength, and the sintered body can not be used at a high temperature for a long time.
Further, Japanese Patent laid open Nos. 55-126,574, No. 59-78,972 and 62-187,174 disclose that when Si.sub.3 N.sub.4 is added to Al.sub.2 O.sub.3, the strength, toughness and hardness are increased in the resulting Al.sub.2 O.sub.3 sintered body dispersing Si.sub.3 N.sub.4 particles dispersed therein or in the resulting sintered body in which Al.sub.2 O.sub.3 particles are dispersed into a sialon matrix. In these sintered bodies, however, the high temperature properties are not mentioned at all, or the satisfactory increase of the strength and toughness can not be achieved, or the high-temperature strength can not be expected due to the presence of sintering aids such as spinel or the like.